I think he's having these feelings because of the thought of what's going on. So far, to his knowledge, since the begining of the relationship he's had her all to himself to kiss and all that. To me (yea I'm young but who cares) kissing is very passionate, and if my girlfriend had sex with another girl, I think the kissing and being intimate in those ways would bother me more than the more hardcore acts.

If he saw how they were doing this, maybe he'd be more comfortable. If I saw my girl kissing her any differently than she kisses me I know I'd be like 20 times more comfortable.